Fuel injection system

ABSTRACT

Disclosed is a fuel injection system, in particular a common rail system, for fuel delivery in internal combustion engines, in particular diesel engines of commercial vehicles, with a low pressure circuit in which at least one low-pressure feed pump supplies fuel from a fuel tank to a high-pressure pump which supplies the highly pressurized fuel to a central high-pressure fuel reservoir. In order to simplify the ventilation of the low-pressure circuit, a device is provided for intentionally decreasing the pressure in the low-pressure circuit.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a 35 USC 371 application of PCT/DE 00/03797 filed onOct. 27, 2000.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates to a fuel injection system, in particular a commonrail system, for fuel delivery in internal combustion engines, inparticular diesel engines of commercial vehicles, with a low pressurecircuit in which at least one low-pressure feed pump supplies fuel froma fuel tank to a high-pressure pump which supplies the highlypressurized fuel to a central high-pressure fuel reservoir.

2. Description of the Prior Art

In diesel engines, air is taken in and compressed. At the end of thecompression stroke, highly pressurized fuel is injected into thecombustion chamber, where the mixture of fuel and air self-ignites.

In common rail fuel injection systems, the high-pressure pump, with theaid of the presupply pump, supplies the fuel to be injected from a tankto the central high-pressure fuel reservoir, which is referred to as thecommon rail. Fuel lines lead from the rail to the individual injectors,which are associated with the cylinders of the internal combustionengine. The motor electronics trigger the injectors individually as afunction of the operating parameters of the internal combustion enginein order to inject fuel into the combustion chamber of the engine.

When the fuel tank is emptied or after maintenance work, thelow-pressure circuit is filled with air. In conventional fuel injectionsystems, the air in the low-pressure circuit must be fed through thehigh-pressure pump into the high-pressure fuel reservoir, counter to theopening pressure (approx. 1.5 bar) of the intake valve of thehigh-pressure pump. From there, the air can escape via a return line.This venting counter to the opening pressure of the intake valve takes avery long time with conventional low-pressure feed pumps.

In order to accelerate the venting process, low-pressure feed pumps witha larger feed volume could be used. However, low-pressure feed pumps ofthis kind would be grossly oversized for normal operation. As a result,the fuel flow supplied by a low-pressure feed pump of this kind wouldhave to be throttled during normal operation.

SUMMARY OF THE INVENTION

The object of the invention is to simplify the venting of thelow-pressure circuit of a conventional fuel injection system. The fuelinjection system according to the invention should also be simplydesigned and inexpensive to produce.

In a fuel injection system, in particular a common rail system, forsupplying fuel to internal combustion engines, in particular dieselengines of commercial vehicles, with a low pressure circuit in which atleast one low-pressure feed pump supplies fuel from a fuel tank to ahigh-pressure pump which supplies the highly pressurized fuel to acentral high-pressure fuel reservoir, the object is attained by virtueof the fact that a device is provided for intentionally reducing thepressure in the low-pressure circuit.

ADVANTAGES OF THE INVENTION

As a result, the pressure in the low-pressure circuit can be reducedduring venting. This offers the advantage that the air disposed in thelow-pressure circuit can be displaced in a justifiable amount of timeusing a conventional low-pressure feed pump that is not oversized.

A particular embodiment of the invention is characterized in that thelow-pressure circuit is connected to the tank by means of a return linein which a throttle is provided. The venting of air from thelow-pressure circuit into the tank takes place by means of the throttle.This has the advantage that no large counterpressure has to be overcomeduring the venting.

Another particular embodiment of the invention is characterized in thatthe throttle is integrated into an overflow valve which is provided inthe return line. The throttle can, for example, be embodied in the formof an intentionally leaky valve seat or as an additional throttle bore.Integrating the throttle into the overflow valve decreases costs.

Another particular embodiment of the invention is characterized in thata venting bore with a vent screw is disposed at the highest point of thelow-pressure circuit after assembly, particularly in a metering unit forthe high-pressure pump. The air in the low-pressure circuit can escapeinto the atmosphere via the manually operable vent screw. Thisembodiment type has the advantage that it is particularly inexpensive toproduce because of its simplicity. The venting bore must be situated sothat possibly escaping fuel can be collected in a container.

Another particular embodiment of the invention is characterized in thatthe venting screw has a flattening in the thread region, which permitsfuel to pass through the venting bore when the venting screw is turnedslightly. This prevents the fuel from spurting out in an uncontrolledmanner at the beginning of the venting procedure.

Another particular embodiment of the invention is characterized in thatthe high-pressure pump is equipped with a metering device that has asolenoid valve which, when supplied with current, opens a connectionbetween the low-pressure circuit and a return into the tank. Normally,the solenoid valve is closed while the internal combustion engine isbeing started. When the solenoid valve is supplied with current for ashort time during venting, the air in the low-pressure circuit canescape into the tank.

Other advantages, characteristics, and details of the invention ensuefrom the following description in which three exemplary embodiments ofthe invention are described in detail in conjunction with the singledrawing figure which shows a hydraulic connection diagram of a fuelinjection system according to the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

For the sake of simplicity, three different embodiments of the currentinvention are shown by way of example in the accompanying figure. Thehydraulic connection diagram will be discussed first below. Subsequentto that, the three embodiments of the invention will be discussed indetail.

Fuel travels from a fuel tank 1, through a line 2, into a cooling body3. The fuel travels from the cooling body 3, via a line 4, to a handpump 5. A check valve 6 is connected in parallel with the hand pump 5.The check valve 6 constitutes a bypass which is opened, for example,when the hand pump 5 is damaged or clogged.

After the hand pump 5, a mechanically driven presupply pump 7 isdisposed in the line 4. Parallel to the mechanically driven presupplypump 7, there are two check valves 38 and 39 disposed in opposition toeach other. The check valves 38 and 39 assure that the presupply pump 7is bypassed in the event of a particular pressure difference.

After the presupply pump 7, a fuel filter 8 with a water separator isdisposed in the line 4. A bypass line (not shown) with a check valve canbe connected in parallel with the fuel filter 8.

The fuel supplied by the hand pump 5 or by the mechanically orelectrically driven presupply pump 7 travels through the line 4 and aline 9 to a high-pressure pump 10. The high-pressure pump 10 includestwo high-pressure pump elements 11 and 12, in which high pressure isexerted on the fuel supplied by the presupply pump 7 or the hand pump 5.

High-pressure lines 13 and 14 which contain check valves 15 and 16 leadfrom the high-pressure pump elements 11 and 12. The high-pressure lines13 and 14 connect the high-pressure pump elements 11 and 12 to a centralhigh-pressure fuel reservoir 17. Arrows 18, which lead from thehigh-pressure fuel reservoir 17, indicate a connection to the individualinjectors (not shown) of the internal combustion engine to be fed.

The line 9 contains a quantity regulating valve 19, e.g. of the kinddescribed in DE 197 25 472, on which U.S. Pat. No. 5,996,556 relies forforeign priority, the disclosure of which is hereby incorporated byreference. The quantity regulating valve 19 can connect the line 9 to areturn line 24 which feeds into the fuel tank.

The line 4 is also connected to a line 20 which contains a throttle 21.The line 20 can be connected to the return line 24 by means of a 2/2-waysolenoid valve 22. When a control unit (not shown) temporarily opens thesolenoid valve 22, air possibly contained in the low-pressure circuitcan escape into the fuel tank 1 via the line 20 and the return line 24.

Furthermore, the line 4 is connected to the return line 24 by means of aline 25 which contains a check valve 26. According to a secondembodiment of the invention, a throttle 27 is connected in parallel withthe check valve 26 and permits air possibly contained in thelow-pressure circuit to escape into the fuel tank 1.

Finally, according to a third embodiment of the invention, the line 4 isconnected to a line 34 which feeds into a container 35. The line 34suggests a venting bore, which can be closed by means of a vent screw36.

Finally, it should be noted that the high-pressure fuel reservoir 17 isconnected to the cooling body 3 by means of a return line 30 thatcontains a check valve 31.

The quantity regulating valve 19 and the 2/2-way solenoid valve 22constitute a metering unit for the high-pressure element 12. Thehigh-pressure element 11 also requires a metering unit of this kind, butthis unit is not depicted for the sake of clarity.

The foregoing relates to preferred exemplary embodiments of theinvention, it being understood that other variants and embodimentsthereof are possible within the spirit and scope of the invention, thelatter being defined by the appended claims.

We claim:
 1. In a fuel injection system, in particular a common railsystem, for fuel delivery in internal combustion engines, with a lowpressure circuit (1-9) in which at least one low-pressure feed pump (5,7) supplies fuel from a fuel tank (1) to a high-pressure pump (10) whichsupplies the highly pressurized fuel to a central high-pressure fuelreservoir (17), the improvement comprising pressure reducing means forintentionally decreasing the pressure in the low-pressure circuit (1-9),wherein the low-pressure circuit (1-9) is connected to the tank (1) bymeans of a return line (24, 25) which contains a throttle (27), and thethrottle (27) is integrated into a check valve (26) which is provided inthe return line (25).
 2. In a fuel injection system, in particular acommon rail system, for fuel delivery in internal combustion engines,with a low pressure circuit (1-9) in which at least one low-pressurefeed pump (5, 7) supplies fuel from a fuel tank (1) to a high-pressurepump (10) which supplies the highly pressurized fuel to a centralhigh-pressure fuel reservoir (17), the improvement comprising pressurereducing means for intentionally decreasing the pressure in thelow-pressure circuit (1-9), wherein said pressure reducing means includea venting bore (34) with a vent screw which is disposed at the highestpoint of the low-pressure circuit (1-9) after assembly of the system. 3.The fuel injection system according to claim 2, wherein the ventingscrew has a flattening in the thread region, which permits fuel to passthrough the venting bore (34) when the venting screw is turned slightly.4. In a fuel injection system, in particular a common rail system, forfuel delivery in internal combustion engines, with a low pressurecircuit (1-9) in which at least one low-pressure feed pump (5, 7)supplies fuel from a fuel tank (1) to a high-pressure pump (10) whichsupplies the highly pressurized fuel to a central high-pressure fuelreservoir (17), the improvement comprising pressure reducing means forintentionally decreasing the pressure in the low-pressure circuit (1-9),wherein the high-pressure pump (10) is equipped with a quantityregulating valve (19) that has a solenoid valve (22) which, whensupplied with current, opens a connection between the low-pressurecircuit (1-9) and a return (24) into the tank (1).